If you're looking to format many timestamps all at once, I've written a C util called datefmt that formats timestamps in a text stream:
Let’s say we have some logs that contain unix timestamps:
$ cat logs.txt
EVENTS 1638499687 blahblah log1
EVENTS 1638499717 blahblah log2
We can pipe this log into datefmt to convert these timestamps into human-readable dates:
$ <logs.txt datefmt
EVENTS 2021-12-02 18:48 blahblah log1
EVENTS 2021-12-02 18:48 blahblah log2
Of course you can customize the format as well:
$ <logs.txt datefmt "DATE:'%m-%d %R'"
EVENTS DATE:'12-02 18:48' blahblah log1
EVENTS DATE:'12-02 18:48' blahblah log2
I've packaged this in NixOS, hopefully it will trickle out to other distros soon, but for now you will need to download the tarball and build it with make